1. Field of the Invention
The present invention relates to a mobile communication terminal, communication apparatus, mobile communication method, and communication method for establishing a communication link with a communication partner using PPP (Point-to-Point Protocol).
2. Related Background of the Invention
The IP mobility technique, which supports a channel change pursuant to a change of IP (Internet Protocol) address, is a communication technique for transmitting and receiving packets using a plurality of communication channels. Mobile IP (refer to IETF RFC3344 “IP Mobility Support for IPv4” (Non-Patent Document 1)) is a typical protocol of the IP mobility technique. Mobile IP supports mobility in the network layer, a communication terminal notifies a home agent of an IP address change, and communication is carried out with a communication partner via the home agent. This IP address change process can cause a break in or interruption of communications.
Further, there is also a method called multilink PPP, which combines a plurality of communication links into a single communication link (refer to IETF RFC1717 “The PPP Multilink Protocol (MP)” (Non-Patent Document 2)). In multilink PPP, since a single communication channel is visible as seen from the IP layer 3 protocol, the IP address does not change even when the communication channel is switched. If this multilink PPP is used, IP-wise, a plurality of communication links can be utilized by a single communication channel. However, multilink PPP is normally designed to combine a plurality of low-speed communication links to establish a high-speed link, and is premised on the fact that the quality of all the communication links is consistent.
Methods, which expand this multilink PPP, and which added control functions that allocate packets to communication links of different communications quality have also been proposed (refer to Japanese Patent Application Laid-open No. 2000-216815 (Patent Document 1) and Japanese Patent Application Laid-open No. 2007-60494 (Patent Document 2)). If these methods are used, packets can be efficiently transmitted by combining communication links of different communications quality.